The present invention relates to a multichamber acid compartment two-compartment electrodialytic water splitter and a method of using same to produce an aqueous soluble acidified salt solution and aqueous soluble base at increased current efficiency.
Electrodialytic water splitting in a two-compartment cell is well known. For example, U.S. Pat. No. 4,391,680 by the same inventors, discloses generation of strongly acidified sodium chloride and aqueous sodium hydroxide by two-compartment water splitting of aqueous sodium chloride. However, when generating strong acids in a two-compartment electrodialytic water splitter, the efficiency for acid generation falls rapidly as the concentration of acid in the acid compartment increases due to migration of hydrogen ions across the cation membrane from the acid compartment into the base compartment.
Various methods have been employed in the prior art in an attempt to overcome the decrease in current efficiency with increased acidity in the acid compartment. For example, a three-compartment electrodialytic water splitter comprised of alternating bipolar anion and cation permselective membranes thereby forming alternating acid, salt and base compartments is disclosed in our copending patent application Ser. No. 474,711, filed Mar. 14, 1983. In addition, the staging of two conventional two-compartment electrodialytic water splitters whereby the acidified salt solution withdrawn from the acid compartment of one two-compartment water splitter is fed to the acid compartment of a second two-compartment water splitter is disclosed in our U.S. Pat. No. 4,391,680. In an attempt to increase the efficiency of the bipolar membrane, U.S. Pat. No. 3,111,472 (Oda et al.) discloses disposing a microporous water permeable cation or neutral membrane in the acid and/or base compartments of a three-compartment electrodialytic water splitter. Oda et al. disclose feeding a brine solution to an acid compartment formed by a cation face of bipolar membrane, flowing the aqueous solution through the microporous water permeable membranes separating the acid compartments, and withdrawing an acidified brine solution from the acid compartment nearest the salt zone. However, the apparatus and method of Oda et al. does not overcome the lower efficiency due to migration of the hydrogen ions through the membranes into the salt and/or base compartments.
All of these prior art disclosures require installation of auxilliary equipment and separate additional process steps, both of which increase costs. In view of the foregoing, the industry has endeavored to develop a process capable of producing highly acidic aqueous brine at low cell voltage. To date, this had not been achieved.